Bi-directional interactions with tumor microenvironment enhance BRCA1-IRIS overexpressing TNBC tumor cells aggressiveness. TNBC is an aggressive breast cancer lacks ER/PR expression and Her2 amplification, therefore lacks targeted therapy. TNBC is over-represented in African American women, the majority live in Mississippi. TNBC is an aggressive rapidly advanced disease that metastasizes to lung, liver, and brain. BRCA1-IRIS is upregulated in the majority of TNBC. BRCA1-IRIS overexpression (hereafter IRISOE) promotes formation and metastasis of TNBC tumors, and its silencing prevents both. The objective of this study is to identify the molecular mechanism(s) responsible for enhanced metastasis by IRISOE. Our central hypothesis is that due to massive proliferation triggered by IRISOE, IRISOE tumors become avascular and necrotic in their cores. Hypoxia developed in areas surrounding these necrotic cores (we refer to this necrotic/hypoxic core as the aggressiveness niche) aggravates IRISOE tumor cells metastatic ability. Our data show that in the niche, hypoxia triggers IRISOE/TNBC tumor cells to secrete IL-6 and that induces IL-6R expression on MSCs. This signaling loop attracts MSCs to the vicinity of IRISOE/TNBC tumor cells and activates them to secrete PGE2. PGE2 binds to IRISOE/TNBC tumor cells through EP2/4 re-activates IRISOE/TNBC tumor cells to secrete other cytokines, e.g., GM-CSF and VEGF. GM-CSF is a potent recruiter of monocytes and VEGF of endothelial cells (EC). GM-CSF binding to CSF-2R on tumor associated macrophages (TAMs) and VEGF binding to VEGFR on ECs recruit them to the vicinity of IRISOE/TNBC tumor cells and activates them to secret factors, such as TGF-1 from TAMs and IL8 from ECs. TGF-1 binding to TRI/II and IL8 to CXCR1/2 on IRISOE/TNBC tumor cells, in addition to PGE2/EP2/4 enhance IRISOE/TNBC cells aggressiveness and their dissemination and metastatic potential. In Specific Aim One, we will validate the bidirectional interactions between IRISOE/TNBC tumor cells and MSCs promoting IRISOE/TNBC tumor cells aggressiveness. In Specific Aim Two, we will validate the bidirectional interactions between IRISOE/TNBC tumor cells and M2- TAMs promoting IRISOE/TNBC tumor cells aggressiveness. Finally in Specific Aim Three, we will validate the bidirectional interactions between IRISOE/TNBC tumor cells and ECs role promoting IRISOE/TNBC tumor cells aggressiveness. The proposed studies are in line with the aims of the NIH of generating better understanding of the mechanisms that drive breast cancer progression and produce validated biomarkers for early detection and therapeutic targets. We believe our grant fulfills all these criteria and provide a compelling therapeutic rationale for th development of anti-BRCA1-IRIS drug to specifically target TNBC tumor cells in patients with high risk of recurrence and poor prognosis.